1. Field of the Invention
This invention relates to a plastic package for packaging a element, e.g. IC, CCD (charge coupled device). More particularly, to a plastic package possessing excellent moisture resistance.
2. Description of the Related Art
A resin package is used for packaging a chip in a semiconductor device. A hollow package comprises a box molded product made of plastic with a lead inserted therein, a semiconductor chip is secured to the internal bottom of the molded product, and a transparent or semitransparent cover called "lid" is used to seal an upper opening of the molded product, thereby fabricating a semiconductor device. This hollow package is a type of plastic package.
Semiconductor devises are used by incorporating it into electronic products such as a video camera. Therefore, strict moisture resistance is required for such a semiconductor device so that a semiconductor chip stored in electronic products always works in a normal manner. For that, the hollow package which corresponds to a container in a semiconductor device necessarily has excellent moisture resistance for a long period of time such that it can withstand a severe test such as a pressure cooker test.
Improvements in plastic compositions constituting the resin package body have been made to raise the level of the moisture resistance of the hollow package. For instance, there has been a trial to convert the chemical structure of an epoxy resin to various modified structures from the basic structures such as a novolak type, bisphenol type, or the like. However, this trial unnecessarily satisfies improvements in the moisture resistance. Also, other ingredients constituting the plastic composition, for example, a mold release agent for improving the releasability from a metal mold and various fillers added to control the coefficient of thermal expansion and the heat conductivity can insufficiently contribute to the improvement in the moisture resistance of the hollow package even if the sorts or amounts of these are adjusted.
In order to solve these problems, a trial is made in Japanese Patent Application Laid-Open (JP-A) No. 8-55927 which describes "As a result of various studies to improve the moisture resistance of a hollow package, it has been found that there is the cause controlling the moisture resistance of the hollow package in the condition of the boundary between a lead and a plastic layer. Specifically, it was clarified that a hollow package which has adhesiveness between the lead and the plastic layer can be obtained with an increase in moisture resistance in long time use". Based on these fact, Japanese Patent Application Laid-Open (JP-A) No. 8-55927 discloses a hollow package comprising a plastic package body having a concave portion for storing a chip; and a lead including one end extending to the concave portion, the other end protruding from the package body, and an intermediate portion embedded in the package body, the one end being electrically connected with the semiconductor element, wherein the intermediate portion of the lead is formed so as to have a roughened face. This structure results in achieving a relatively long durability in terms of a durable time in pressure cooker test as long as 14 hours.
The rough face is formed in the intermediate portion of the lead by a sand blast method in which the intermediate portion of the lead is processed by air blast using alumina micropowder to form a rough face on the lead.
Such a sand blast method for forming the rough face on the lead, however, has the problem that it requires troublesome operations for sufficiently removing alumina micropowder attached to the surface of the lead. This method also has the drawback of non-uniformity of the roughened face condition caused by the accumulation of polished powder on the surface of a metal mask used for a lead frame. Further, this method imparts cost problems including a great cost of expendable supplies such as a metal mask for lead frame, alumina polishing powder, and the like and a great maintenance cost associated with the troubles of a sand blast apparatus itself, a compressor, or the like caused by the polishing powder.
On the other hand, there is a greatly increased demand for the provision of the moisture resistance of the hollow package in a semiconductor device including a CCD. It is required in practice to achieve an increase in durable time in a pressure cooker test. It is also required to develop a new process for manufacturing an inexpensive hollow package having excellent moisture resistance since there are exacting demands of a more inexpensive hollow package.